Laboratory Study Displacement Efficiency of Viscoelastic Surfactant

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Laboratory Study Displacement Efficiency of Viscoelastic Surfactant Solution in EOR Ke-xing Li, Xueqi Jing, Song He, Hao Ren, and Bing Wei Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.5b02925 • Publication Date (Web): 10 May 2016 Downloaded from http://pubs.acs.org on May 14, 2016

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Laboratory Study Displacement Efficiency of Viscoelastic Surfactant Solution in EOR Ke-xing Li*†§; Xue-Qi Jing§; Song He‡; Hao Ren‖, Bing Wei*†§ †

State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation(SWPU),Chengdu,China

§

School of Petroleum and Natural Gas Engineering,SWPU,Chengdu,China

‡

Dagang Oilfield Branch PetroChina,Tianjing,China

‖)

Xinjiang Oilfield Branch PetroChina ,Karamay,China

Abstract: Polymer/surfactant combination solutions were easy to suffer chromatographic separation effect when injected into a relatively low permeability reservoir, for the poor injection ability. In addition, the long chain polymer molecules are easy to be cracked when passing through the porous media with low pore throat radius. These problems limit the polymer/surfactant combination flooding used in the poor reservoirs for EOR(Enhanced Oil Recovery). The conventional VES is mainly used in fracturing or drilling. In this paper, we present a novel viscoelastic surfactant—VES-JS which is designed for EOR. It has an unique ability that allows it has visco-elasticity like the polymer solution and the capacity to deduce the IFT value of oil and water to order 10-2~10-3mN/m. For the self-assemble ability, it can reform network structure when it stiff in the porous media. Under the reservoir condition-65℃， 100×10-3μm2,VES-JS shows good visco-elasticity and ultra low IFT which can improve the displacement efficiency. An experimental investigation of VES flooding was conducted by series of core flooding. The effects of reservoir permeability, VES concentration, injection rate, injection volume, injection time, and reservoir heterogeneity on displacement efficiency were evaluated. The results indicate that under the experiment conditions, VES flooding can improve the oil recovery ratio from 10.64% to 24.72%. Moreover, under the comparable experiment conditions, VES flooding can get recovery increment 17.18% , while polymer flooding is 10.56% and surfactant flooding is 8.64%,which is close to ratio of the polymer/surfactant combination flooding 17.35%. These exciting results show a strong potential for the VES used in relatively low permeability reservoirs for EOR.

1. Introduction There is a lot of oil still remaining in the reservoirs when at high the water cut. Chemical

floods

-surfactant,

polymers

and

sometimes

ACS Paragon Plus Environment

alkali

(Mahdi

Kazem-

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pour,2012;Zaitoun,2012;Haiyan Zhang,2012;Y.P.Zhang,2007)1-4 have become more and more attractive in recent years. Polymer solution is a typical viscoelastic fluid(H.J.Yin,2012)5.The elastic stress causes the protruding portion residual oil to change shape and move(D.Wang,2007)6. Research showed that high elasticity polymer solution resulted to higher sweep efficiency and lower residual oil saturation compared with low elasticity polymer solution (Urbissinova,2010;Zhang,2008)7,8. Recent years, the theory that viscoelastic fluid can improve the oil recovery has been steadily accepted, the higher the visco-elasticity, the higher the oil recovery (Wu Wenxiang,2007;Jiang,2008; Morvan,2012;G.Degre,2012)9-12. But there are a lot of poor reservoirs still not be exploited efficiently. One of the main difficulties is the poor injectivity and productivity (Cheng,2007)13. Viscoelastic surfactant-VES has remarkable visco-elasticity character due to the ability of forming wormlike micelles and entangled structures(Yu,2009)14. As a result, VES has good flow ability, can dramatically increase the viscosity of the displacing fluid and lower the IFT value of oil and surfactant. So we can use VES to control the mobility in low-tension water flooding(Istvan Lakatos,2007)15. Their viscoelastic behavior is due to the overlap and entanglement of long wormlike micelles(Merve R,2013)16 .In straight tubing experiments, fluid concentration and pipe shear are both having notable effects on fluid elasticity(Kamel,2010)17. VES has been developed to take place of polymer solution in a board range of reservoir conditions with good injectivity even when using very viscous VES solutions( ie. up to 1000mPa.s) and low permeability reservoir. A series of core-flood experiments showed the surfactant combined with a conventional low concentration polymer solution can reduce the residual oil saturation 10%~15%(Morvan,2012;G.Degre,2012)11,12. To investigate the VES flowing through step expansion-contraction size pores, a dynamic model was developed, and it was illustrated that the density of micelles became non-uniform(Stukan,2008)18. A higher recovery achieved by VES displacing(J.V.Santvoort,2015)19. The problem with these surfactants is that they are expensive and used at low temperature less than 200℉(93.3℉). A VES for EOR was introduced which exhibited a viscous phase at low concentration(0.1% to 0.3% w/w) and relatively high temperature(80℉) (Mikel Morvan,2009)20. Studies illustrate that the addition of nanoparticles-MgO or ZnO improved the thermal stability of VES micellar structures in CaBr2 and CaCl2 brines up to 275℉(135℉) and showed an improved viscosity yield at different shear rates(Merve R,2013)16. Series VES fluids have been developed that the temperature range has been extended to 300℉（James


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B,2008）21and have good stability in 18.6% highly saline brine(Siggel,2012)22. Additionally, fluid-loss controlling technology improves the performance of VES(Huang,2007)23.

2. Materials and Experiment 2.1. Chemicals A viscoelastic surfactant called VES-JS was achieved by mixing a cationic surfactant and a long chain unsaturated amide betaine at a certain ratio. Compared with the conventional VES used in fracturing, VES-JS not only has strong viscoelasticity, but also has good ability to reduce the oil-water IFT to a low order10-2~10-3mN/m. For it’s low molecule weight structure, VES-JS is theoretically more easy to inject than polymer. In this investigation the VES sample’s concentration is 25%, and diluted to a series of low concentrations. 2.2. Crude Oil and Brine Sample Oil sample used in the experiment was from W2 reservoir in Jiangsu Oil Field. The density of crude oil was 817 kg/m3. Meanwhile, at the reservoir temperature of 65℃, the viscosity of which was around 9.39 mPa·s. Water used in study was simulated from W2 formation water total salinity data, and the W2 reservoir formation water composition was listed in Table 1. 2.3. Core samples In the target oil reservoir of W2, the temperature and average permeability are 65℃ and 90×10-3µm2 severally. Artificial sinter cores which are mainly made of SiO2 were applied in the oil displacement experiments. Cores are 3.8 cm in diameter and 7 cm length. Moreover, permeability for most of the cores are about 100×10-3 µm2. In order to characterize the effect of the reservoir heterogeneity, a small amount of cores, whose permeability is less than 10× 10-3 µm2 or more than 2000× 10-3 µm2, were used in the experiment. 2.4. Interfacial Tension Measurements The TX-500C SpinningDrop Interface tensiometer was used to measure oil-water interfacial tension. The oil-water interfacial tensions between W oil sample and VES-JS were obtained at the temperature of 65℃. 2.5. Rheometry Measurements Using the HAAK MARSIII rotary rheometer, rheological parameters for viscoelastic surfactant solution were determined. Under frequency 0.01-10 Hz, storage modulus and loss


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modulus of three different concentrations of VES solution were tested at 65℃ . According to the measured parameters, the relaxation time and tangential loss angle were calculated, and then the type of the viscoelastic fluid was determined. 2.6. Micro-structure Measurments The Quanta450 environmental scanning electron microscopy was applied in this study to the characterize the microstructure of VES under different salinity. 2.7. Core Displacement Experiments Compared the polymer, conventional surfactant and polymer/ surfactant composite system in oil displacement experiments, the effect of displacement of viscoelastic surfactant solution in EOR was analyzed. The experiments were completed in the core displacement device, which can keep the temperature at 65℃ and benefit to simulate reservoir conditions. The flow chart is depicted in Fig.1. The core parameters are shown in Table 3. The core flooding experiment steps are as the following: (1)Core cleaning and putting them into the oven at 65℃ for several hours until the cores weight are not decrease, then measure the cores dry weight. Measure the absolute permeability(Kg.). Saturating the cores with brine, and calculate the pore volume and porosity. (2)Putting a core into the core holder and mount the flooding cell, then put the equipment in oven at reservoir temperature 65℃ . Injection of W2 crude oil until irreducible brine saturation(Swi), calculation of Soi by formula Soi=1- Swi. (3)At Swi, injecting reservoir brine at a steady flow rate until the water cut of core holder output raising to 98%. Meanwhile collection of the output oil, measurement of initial water flooding recovery. (4)Injection of the flooding agent as the experiment designed. Collection of oil from the output, measurement of the oil volume and calculation of the recovery increment. (5)Subsequent water flooding, collection of oil from the output until the water cut raising to 98%.Measurement of the oil volume in this step, calculating the recovery increment and the recovery in the whole experiment procedure.

3. Results and Discussion 3.1. Viscosity and IFT Fig.2 shows the variation of apparent viscosity and oil-water interfacial tension for VESJS with the increase of concentration under the 65℃ and TDS of 25830.2mg/L.


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As the IFT curve shows in figure 2, the IFT value decrease when VES concentration is lower than 3000mg/L. The oil-water IFT can maintain in order 10-2~10-3mN/m when the concentration is between 3000mg/L~4200mg/L. When the concentration is higher, the IFT value increases, at 10000mg/L IFT rise to 5.1×10-1mN/m. The viscosity curve indicates that the viscosity accelerated when the concentrations of VES - JS is over 3000mg/L, and the viscosity at 10000mg/L is 69.4mPa.s. The results illustrate that a concentration range exists if we want to achieve a balance between increasing viscosity and decreasing to order 10-2~103

mN/m ultra low oil-water IFT . Taking into account the retention loss of VES in reservoir condition, the VES concentra-

tion above 3000 mg/L will be used in the following tests and experiments. 3.2. Viscoelastic Property Modulus curves

Fig.3 indicates the changes of VES-JS solution modulus with frequency under different concentration, while the correlations of solution modulus and frequency under different salinity are shown in Fig.4. The higher the concentration is, the greater of the modulus value and more significant characteristics of viscoelasticity. With the concentration rising up, the intersection of G'=G'' moves to right. It indicates that the VES-JS solution show significant viscoelasticity with the concentration increasing .In addition, at the left of the intersection, the tangential loss angle is greater than 1.0 and viscosity performance more significantly than elasticity; in contrast, at the right of the intersection, the tangential loss angle is less than 1.0 and elasticity is more obvious than viscosity. Fig.4 shows that with the increase of salinity, storage modulus and loss modulus of VES - JS solution overall increase and the corresponding frequency of intersection point declines. In the experimental salinity range, the existence of salinity makes the VES-JS solution shows elasticity characteristics under lower shear frequency, for that the structure of aggregates formed by VES-JS is more stable in relatively higher salinity. The microstructure of VES-JS under different salinity are shown as Fig.5. It proved that with the increase of salinity, the VES structure is more dense. Fig.6 illustrates that polymer and polymer/surfactant have comparable rheological properties. For VES-JS the frequency is only 0.1Hz when G'>G'', while polymer/surfactant need about 5Hz. This illustrates that VES is more likely to exhibit viscoelastic properties under shear stress at comparable viscosity. Relaxation Time


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Giving the curves of storage modulus versus frequency and loss modulus versus frequency, the two curves intersect. Generally, the characteristic time (relaxation time) of solution is defined as the inverse of the corresponding frequency ωc of intersection. Finally, the intersection modulus of relaxation time, intersection angular frequency and corresponding relaxation time are acquired and listed in Table 2. Results show that with the increase of VES-JS solution concentration, intersection modulus increases and relaxation time reduces. The reason is that VES-JS solution is the compound of cation and anion surfactant , and ion pairs were formed each other. But there don't develop intertwined network structure and peristalsis of molecular chains aren't hindered. Therefore, the greater the concentration is, the more neutralization of cation-anion and the shorter the relaxation time. Flow Pattern

By measuring the rheological curve, the fluid type can be determined as well as calculating the basic rheological parameters. The flow curves of pseudo-plastic fluid and dilatant fluid are nonlinear, which belongs to the power-law fluid. The correlation between shear stresses τ and shear rate (dγሶ/dt) can be expressed by the formula (1) of power-law fluid: τ = Kγሶ ୬

(1)

K, consistency coefficient, reflects the levels of system viscous; non-newtonian coefficient n, shows the deviation degree of Newtonian fluid properties. When n < 1 as pseudoplastic fluid, when n > 1 for expansion fluid and n = 1 for Newtonian fluid. Taking the exponential on both sides of equation (1), there is a linear relationship between shear rate and shear stress in double logarithmic coordinates from Fig.6. The slope represents nonnewtonian coefficient n, and the intercept is a logarithmic of consistency coefficient K. Using deionized water to make up 5000 mg/L of solution, the double logarithmic rheological curve of VES-JS solution was measured (Fig.7). The consistency coefficient measured is 0.044Pa.sn and non-Newtonian coefficient is 0.52.

It is a pseudoplastic fluid. 3.3 Displacement Effect Factors In the core displacement experiment, the VES - JS solution acts as a displacing agent. The influences of reservoir permeability, VES concentration, injection flow rate, injection volume(PV), injection time and reservoir heterogeneity on displacement efficiency were studied, under the condition of 65 ℃ and salinity 25830.2 mg/L. Permeability V.S. Recovery Increments


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After initial water flooding, 0.3 PV of 5000 mg/L VES-JS solution was respectively injected into cores with different permeability. Then second water flooding to 98% of water cut again. The results are shown in Table 4 and Fig.8. The experimental results shows that the growth of recovery ratio caused by VES-JS rapidly increase in the first half of the curve, and then became nearly flat with the permeability increases. When the core permeability is less than 500×10-3µm2, the VES has a great influence on recovery ratio increment with the increase of permeability; but there is no obvious effect on recovery as over 500×10-3µm2. The reason for this phenomenon may be that there is a matching relationship between the size of VES aggregates and the pore throat radius. There are different pore throat radiuses in different permeability cores. When the size of aggregates for VES solution is greater than the pore throat radius, it will be easily sheared into small molecules by pore throat and the viscoelasticity disrupted, so the corresponding increase of recovery efficiency is low. The VES aggregates can maintain visco-elasticity when the size is less than the pore throat radius, then the corresponding recovery ratio increase rapidly with the permeability increasing. However, the aggregate size of VES at a certain concentration is steady, if the pore throat radius rise to a value larger than it, there will be no obvious effect on the visco-elasticity, then the corresponding recovery curve shows smooth. Concentration V.S. Recovery Increments After water flooding, 0.3PV of VES-JS solution was injected into comparable permeability cores with different concentrations. Subsequently, the second water floods to 98% of water cut . The experiment results are shown in Table 5 and Fig.9. The increment of the recovery ratio can be tuned by varying the surfactant concentration(J.V.Santvoort,2015)19.It indicates that as the concentration of VES solution is below 5000 mg/L, the recovery increment increases with the adding of concentration; in contrast, after the concentration is greater than 5000 mg/L, the recovery increment achieves stable. The reasons may be that the increase of concentration could overcome the disruptive effect of micelle-hydrocarbon interaction and promote the volume of VES aggregate, which enhances the carrying capacity. But after the aggregate volume goes up to some extent with concentration rising, the shearing action improves and the size of VES aggregate no longer increases, which leads to a steady recovery increment. Therefore, the minimum concentration of VES-JS designed to flood is about 5000 mg/L which can bring better effect than lower concentration for reservoir W2 as Fig.9 shown.


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Flow rates V.S. Recovery Increments Under the same conditions, 0.3PV of VES solution, whose concentration is 5000 mg/L, was injected into cores in different flow rates. The cores of comparable permeability(100×103

µm2) were used for the different flow rates. The influence of flow rate on the displacement

efficiency of VES was exhibited in Table 6 and Fig.10. As the displacement rate was lower than 0.5cm3/min, enhancement of velocity can contribute to recovery. After the injection rate adds to some degrees (bigger than 0.5cm3/min), the recovery increment don't significant change. Combined the results of rheological tests, it illustrates as displacement rate goes up, shearing to VES enhances and the elastic characteristics is more obvious, which results in carrying more residual oil. Nevertheless, after the injection rate increases to certain degree, the aggregation structure of VES was broken to make recovery increment stabilized. Injection Porous Volume V.S. Recovery Increments

In the same condition, VES solution, whose concentration is 5000 mg/L, was injected into cores at the flow rate of 0.5cm3/min. The results are listed in Table 7, and relationship of PV values of injection VES solution and displacement efficiency is shown in Fig.11. With the increase of VES injection, the corresponding curve of recovery growth rises integrally, but increment is more and more small. After the injection volume is more than 0.5 PV, the recovery increment of curve becomes flat, and increasing injection has little contribution to recovery ratio increment. Some reasons may relate to it. Firstly, as the PV of injection VES increases, sweep efficiency increasing. But, the increase of sweep efficiency tends to small when the injection VES volume rising to a certain value. The results indicate the suitable injection volume of VES should be no more than 0.5 PV under W2 reservoir condition. Water cut V.S. Recovery Increments Under the same conditions, the displacement experiments of VES after water flooding to water cut of 30%, 60% and 98% respectively. The results are shown in Table 8 and Fig.12. The experimental results show the great recovery increment brought by VES flooding is 19.38%~22.19%, but the recovery growth difference on three water cut are within 3%, which states that the injection time does not have obvious effect on the VES displacement. Heterogeneity V.S. Recovery Increments The cores with different permeability are paralleled to model a reservoir having permeability quotient. In the parallel experiments, during water flooding, VES injection and subsequent water flooding, the liquid is collected at the outlet of the low permeability and high


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permeability cores respectively. Table 9 lists the displacement results of VES in heterogeneity reservoir at the speed of 0.5 cm3/min and other comparable conditions. The results reveal that when the layer of heterogeneity exists, the VES solution injected was prior to enter the relative high permeability cores, and relative low permeability cores don't enter liquid. It can be observed in the experiments that the injected water leak out from high permeability layers and recovery growth mainly comes from the high permeability cores at later stage of water flooding. Therefore, the VES solution used in our experiments isn't of a function of adjusting water injection profile like polymer. The reason is that injection rate is low and the linear flow is absolutely dominant, so the shearing force is main in VES solution, leading to aggregate structure was damaged into small molecules and easier to enter the high permeability layer. The results show that it is necessary to adjust the vertical injection profile before VES displacement in the strong vertical heterogeneity reservoir to obtain better effects. 3.4 Comparing efficiency of oil displacement for different EOR methods For further evaluating the feasibility of visco-elastic surfactant solution in EOR, the displacement results of VES-JS, surfactant, polymer and polymer/ surfactant combine flooding were compared on the same experimental conditions. At the same time, the oil-water interfacial tension and the apparent viscosity of the VES - JS solution(5000mg/L) listed in Table 10 were measured under 65℃ and salinity of 25830.2mg/L. In the contrasting experiments, the HPAM concentration was determined with it’s viscosity close to the VES-JS. And a surfactant concentration was of similar order of oil-water interfacial tension close to VES-JS, as well as the oil displacement experiment of the polymer/ surfactant, listed in Table 10. Experiments of oil displacement were conducted on same conditions(shown in Table 11). As listed in Table 11, under a comparable experiment condition, the oil recovery can be enhanced in W2 reservoir by 8.64% after injecting 0.3 PV ordinary anionic surfactant of PS11, polymer (PAM-11) improved 10.56%, while VES and polymer/ surfactant can improve oil recovery above 17%. Under the experimental conditions, VES - JS showed high displacement efficiency like polymer/ surfactant.

4. Conclusions VES can sharply lower oil-water interfacial tension to order 10-3 mN/m and simultaneously possess apparent ability of increasing displacement phase viscosity. The EOR viscoelastic surfactant used in this study illustrates obvious viscoelastic properties. In the study, within the salinity of W2 reservoir water(25830.2mg/L), the presence of inorganic salts make VES aggregates more stable and is helpful to enhance the viscoelastic property.


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The displacement experiments show the ability of displacement efficiency for VES in certain reservoirs like W2, the increment of recovery is 10.64%~24.72%. Meanwhile, on a comparable experiment condition, it’s displacement efficiency is greater than polymer and surfactant, and is similar with polymer/ surfactant binary system. Therefore, this study indicated that VES has good application prospect in EOR.

Author Information Corresponding Author * Tel.:+86-028-83032040. E-mail: [email protected] (Kexing Li) and [email protected] (Bing Wei) Address: School of Petroleum and Natural Gas Engineering, South West Petroleum University, Xindu, Chengdu,China,610500 Notes The authors declare no competing financial interest. Acknowledgements This work is supported by Open Fund(PLN1513) of State Key Laboratory of oil and Gas Reservoir Geology and Exploitation(SWPU) and Key Subject Construction Project Science Foundation for Young Teachers(P011). The authors also wish to express their thanks to JOECO for providing the oil and brine samples, and thanks Shen Zhiqing for providing the surfactant samples. Nomenclature L=length, cm D=diameter, cm ɸ=porosity Kg=air permeability, 10-3µm2 ωc= frequency Tc= relax time n K=consistency index, Pa.s n=non-Newtonian index

References (1)Kazempour, M.; Sundstrom, E. A.; Alvarado, V. Effect of alkalinity on oil recovery during polymer floods in standstone. SPE International Symposium on Oilfield Chemistry, Society of Petroleum Engineers, 2011. (2)Zaitoun, A.; Makakou, P.; Blin, N. et al. Shear stability of EOR polymers.J. SPE Journal, 2012, 17(02), 335-339.


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(3) Zhang, H. Y.; Dong, M. Z.; Zhao, S. Experimental Study of the Interaction between NaOH, Surfactant, and Polymer in Reducing Court Heavy Oil/Brine Interfacial Tension.J. Energy and Fuels, 2012, 26(6), 3644-3650. (4)Zhang, Y. P.; Sayegh, S. G.; Huang, S. Effect of oil/brine ratio on interfacial tension in surfactant flooding. Canadian International Petroleum Conference, Petroleum Society of Canada, 2007. (5)Yin, H.; Wang, D.; Zhong, H. et al. Flow characteristics of viscoelastic polymer solution in micro-pores. SPE EOR Conference at Oil and Gas West Asia. Society of Petroleum Engineers, 2012. (6)Wang, D.; Wang, G.; Wu, W. et al. The Influence of Viscoelasticity on Displacement Efficiency--From Micro to Macro Scale. SPE Annual Technical Conference and Exhibition. Society of Petroleum Engineers, 2007. (7)Urbissinova, T. S.; Kuru, E. Effect of elasticity during viscoelastic polymer flooding: a possible mechanism of increasing the sweep efficiency.J. Journal of Canadian Petroleum Technology, 2010, 49(12), 49-56. (8)Zhang, L.; Guo, F. Micro-mechanisms of residual oil mobilization by viscoelastic fluids.J. Petroleum Science, 2008, 5(1), 56-61. (9)Wu, W, H. Effect of the Visco-elasticity of Displacing Fluids on the Relationship of Capillary Number and Displacement Efficiency in Weak Oil-Wet Cores. Asia Pacific Oil and Gas Conference and Exhibition,2007. (10)Jiang, H. F; Wu, W. X.; Wang, D. M.The Effect of Elasticity on Displacement Efficiency in the Lab and Results of High Concentration Polymer Flooding in the Field. SPE Annual Technical Conference and Exhibition,2008. (11)Morvan, M.; Degre, G.; Beaumont, J. et al. Optimization of viscosifying surfactant technology for chemical EOR. SPE Improved Oil Recovery Symposium. Society of Petroleum Engineers, 2012. (12)Degre, G.; Morvan, M.; Beaumont, J. et al. Viscosifying surfactant technology for chemical EOR: a reservoir case. SPE EOR Conference at Oil and Gas West Asia. Society of Petroleum Engineers, 2012. (13)Cheng, J.; Sui, X.; Yan, W. et al. Cases studies on polymer flooding for poor reservoirs in daqing oilfield. Asia Pacific Oil and Gas Conference and Exhibition. Society of Petroleum Engineers, 2007.


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Figure 1. The flow chart of displacement device


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10 18

Viscosity IFT

1

14 12 0.1 10 8

0.01

IFT,mN/m

Apparent Viscosity mPa·s

16

6 4

1E-3

2 0 0

1000

2000

3000

4000

5000

1E-4 6000

Concentration,mg/L

Figure 2. Apparent viscosity and oil-water IFT of VES-JS versus concentration

1

0.1

Modulus/Pa

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 20

0.01

5000mg/L G' 5000mg/L G'' 7500mg/L G' 7500mg/L G'' 10000mg/L G' 10000mg/L G''

1E-3

1E-4

1E-5 0.01

0.1

1

10

Frequency/Hz

Figure 3. VES-JS solution modulus curves under different concentration


Page 15 of 20

10

1

Modulus/Pa

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

0.1

0mg/L G' 0mg/L G'' 10000mg/L G' 10000mg/L G'' 25000mg/L G' 25000mg/L G''

0.01

1E-3

1E-4 0.01

0.1

1

10

Frequency/Hz

Figure 4. The modulus curves under different salinity

a. deionized water

b. TDS 10000mg/L

c.TDS 25000mg/L

Figure 5. The microstructure of VES-JS under different salinity(2000×)

Figure 6. Modulus curves of different flooding agents


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0.5

n=0.52 k=0.044Pa.sn

0.0

lgτ

-0.5 -1.0 -1.5 -2.0 -2.5 -2

-1

0

1

2

3

lgγ

Figure 7. The linear fitting of rheological curve for VES-JS solution 30

Recovery Increment/%

25

20

15

10

5

0 0

500

1000

1500 -2

2000

2500

2

Permeability/×10 µm

Figure 8. The increases of recovery efficiency with the permeability changing 30

25


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 20

20

15

10

5

0 0

2000

4000

6000

8000

10000

12000

Concentration/(mg/L)

Figure 9. The increases of recovery with different concentrations of VES solution


Page 17 of 20

30


25

20

15

10

5

0 0.0

0.2

0.4

0.6

0.8

1.0

1.2

Flow Rates/(cm3/min)

Figure 10. The changes of recovery increment with displacement rate 30


25

20

15

10

5

0 0.0

0.2

0.4

0.6

0.8

1.0

1.2

Injection Volume/PV

Figure 11. The correlation between recovery and the PV volume of injection 50

Recovery Increment,%

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

40 30 20 10 0 30

60 Water Cut,%

98

Figure 12. The correlation between recovery and water cut


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 20

Table1. The composition of produced-water from W formation ions

Na++K+

Mg2+

Ca2+

SO42-

HCO3-

Cl-

CO32-

total salinity

content(mg/L)

13497.8

13.8

146.38

504.47

1344.39

10224.2

99.16

25830.2

Table 2. The relaxation time of different concentration VES-JS solution concentration (mg/L) G0 (Pa)

5000

7500

10000

0.0395

0.1236

0.4039

ωc （rad/s）

0.8403

1.8867

2.915

Tc （s）

1.19

0.53

0.3436

Table 3. The core parameters Core No.

L cm

D cm

ɸ

10-2 40-2 40-7 100-1 100-3 100-5 100-8 100-11 100-16 100-25 100-27 100-30 100-31 100-35 100-39 100-40 100-42 100-54 100-70 100-79 100-80 100-81 100-82 300-1 300-6 1000-12 2000-6

6.96 6.99 7.00 6.98 7.00 7.00 7.00 6.98 6.94 6.98 6.98 6.98 6.98 7.00 6.98 6.98 6.98 7.00 6.98 7.00 6.98 7.00 6.98 6.97 6.98 6.99 7.00

3.80 3.79 3.80 3.80 3.79 3.78 3.80 3.80 3.76 3.80 3.79 3.80 3.78 3.79 3.80 3.79 3.80 3.80 3.79 3.77 3.80 3.79 3.80 3.79 3.79 3.79 3.78

0.048 0.185 0.086 0.163 0.162 0.165 0.164 0.175 0.176 0.184 0.147 0.161 0.164 0.172 0.163 0.164 0.185 0.163 0.185 0.176 0.164 0.163 0.161 0.181 0.189 0.202 0.237


×10 µm

Soi %

10 46 38 105 101 102 106 105 98 103 105 99 101 103 103 99 102 102 100 105 106 108 104 314 307 1045 2126

57.0 60.77 55.72 71.04 65.52 67.18 69.23 67.87 64.00 67.12 66.67 68.75 67.69 65.93 71.32 68.46 66.30 65.12 69.48 64.20 67.69 65.12 66.24 69.54 71.67 68.45 70.06

Kg. -3

2

Page 19 of 20

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Table 4. The oil displacement of VES under different permeability Kg.

Core No.

×10 μm

40-2 100-54 300-1 1000-12 2000-6

46 102 314 1045 2126

-3

2

Oil Recovery(Increment) at Different Injection Step,% Water VES Second Water Total Injection Injection Injection Increment 59.26 0 11.11 11.11 55.81 2.38 17.44 19.82 58.73 2.00 21.00 23.00 55.4 1.82 23.63 25.45 53.95 3.03 21.97 25.00

Total Oil Recovery,% 70.37 75.63 81.00 80.85 78.95

Table 5. The results of oil displacement under different concentrations of VES solution Core No.

VES

100-3 100-11 100-54 100-8 100-1

1000 3000 5000 7000 10000

mg/L

Oil Recovery(Increment) at Different Injection Step,% Water VES Second Water Total Injection Injection Injection Increment 46.43 0 5.95 5.95 47.87 2.13 8.51 10.64 55.81 2.38 17.44 19.82 57.78 2.22 17.78 20.00 58.70 2.17 17.30 19.47


Table 6. The efficiency of oil displacement at different velocities Core No.

Flow Rate cm3/min

100-30 100-11 100-54 100-31 100-16

0.1 0.3 0.5 0.7 1.0

Oil Recovery(Increment) at Different Injection Step,% Water VES Second Water Total Injection Injection Injection Increment 52.27 0 13.64 13.64 53.33 0 14.44 14.44 55.81 2.38 16.27 18.65 54.55 2.27 15.91 18.18 50.00 3.75 15.00 18.75


Table 7. The displacement efficiency at different injection volume Core No. 100-39 100-54 100-5 100-70 100-40

PV 0.1 0.3 0.5 0.7 1.0

Oil Recovery(Increment) at Different Injection Step,% Water VES Second Water Total Injection Injection Injection Increment 52.17 1.09 10.87 11.96 55.81 2.38 17.44 19.82 50.00 4.55 18.18 22.73 51.79 7.14 16.07 23.21 49.40 11.48 13.48 24.72

Table 8. The displacement results of VES at different water cut



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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Core No.

Oil Recovery(Increment) at Different Injection Step,% Water VES Second Water Total Injection Injection Injection Increment 47.05 3.57 18.62 22.19 55.10 3.06 16.32 19.38 55.81 2.38 17.44 19.82

Water Cut %

100-70 100-25 100-54

Page 20 of 20

30 60 98

Total Oil Recovery,% 68.62 74.48 75.63

Table 9. The displacement results at different permeability Core No.

Kg. -3 ×10 μm2

40-7 100-27 100-42 300-6 10-2 100-35

46 105 100 300 10 100

K contrast 2.3 3 10

Oil Recovery(Increment) at Different Injection Step,% Water VES Second Water Total Injection Injection Injection Increment 0 0 0 15.51 51.28 5.13 17.95 0 0 0 11.27 40.18 0.9 19.64 0 0 0 17.85 51.11 2.2 20.00

Total Recovery, % 50.00 33.30 58.93

Table 10. The oil-water IFT and viscosity for different agents(65℃,TDS 25000mg/L) Flooding agent

Agent type

5000mg/VES-JS 2000mg/L HPAM 2000mg/L PS-11

VES Polymer Surfactant

2000mg/L PS-11+1500mg/LHPAM

Polymer/Surfactant

oil-water IFT, mN/m 6.1×10-3 2.6×10-3 4.7×10-3

Viscosity, mPa·s 23.4 25.2 25.6

Table 11. The displacement efficiency of different agents Core No. 100-79 100-80 100-81 100-82

Oil Recovery(Increment) at different Injection Step,% Water Agent Second Water Total Injection Injection Injection Increment VES 53.54 3.57 13.61 17.18 Polymer/Surfactant 54.55 3.33 14.02 17.35 Polymer 53.81 0 10.56 10.56 Surfactant 52.47 0 8.64 8.64

Flooding Agent


Total Oil Recovery,% 71.40 71.90 64.37 61.11

Laboratory Study Displacement Efficiency of Viscoelastic Surfactant

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